Lamp unit



y 1 1935- w. UYTERHOEVEN ET AL 2,001,510

' LAMP UNIT Filed March 16, 1954 INVENTORS 966K622 M V BY ATTORNEY Patented May 14, 1935 UNITED STATES PATENT OFFICE LAMP UNIT Application March 16, 1934, Serlal No. 715,951 In Germany April 4, 1933 4 Claims.

The present invention relates to lamp units generally and more particularly the invention relates to such units comprising a gaseous electric discharge lamp device the gaseous atmosphere of 5 which consists of or comprises a metal vapor.

In the United States application Serial Number 715,462, filed March 14, 1934, entitled Gaseons electric discharge lamp devices", the inventors being Mari Johan Druyvesteyn, Willem Uyterhoeven, Cornelis B01 and Martinus van Dam, a lamp unit is disclosed which comprises a heat conservator surrounding a gaseous electric discharge lamp device having a U-shaped tubular container and a gaseous atmosphere therein comprising the vapor of a difiicultly vaporizable metal, i. e., a metal the vapor pressure of which at a temperature of 200 degrees C. is less than 1 mm., such as sodium, potassium, rubidium, cadmium, magnesium, thallium or zinc. In the United States application Serial Number,7l8,241, filed March 30, 1934, entitled Gaseous electric discharge lamp devices, the inventors being Willem Uyterhoeven and Mari Johan Druyvesteyn, a lamp unit is disclosed which comprises a heat conservator surrounding a gaseous electric discharge lamp device having a gaseous atmosphere similar to that mentioned above and an elongated tubular container having curved parts.

The object of the present invention is to increase the luminous efllciency of lamp units of the above type. Still further objects and advantages attaching to the device and to its use and operation will be apparent to those skilled in the art from the following particular description.

We have observed that when the curved part of the container in the above types of lamp devices is of the same cross-section as the other parts of the container the curved part is at a lower temperature than the other parts of the container during the operation of the device. As the pressure of the metal vapor corresponds to the temperature oithe coolest part of the container the low temperature of the curved part of the container has therefore a detrimental effect on the eflloiency of the lamp device since the energy expended in heating the other parts of the container is wasted. We have discovered that this disadvantage is overcome and the luminous efficiency of the lamp unit is increased by making the inside cross-section of the curved part or parts smaller than the cross-section of the straight parts of the tube. When the curved part of the tube is given a smaller cross-section, the voltage gradient and consequently the heat developed in the curved part is increased, in other words, the

heat development in the tube is adapted in a simple manner to the heat emitted by the wall of the tube. The energy consumed for the heating of the wall of the tube is, therefore, utilized to the greatest possible extent whereby the efficiency of the 5 tube is increased. By means of calculations and by some simple tests, the most favorable internal diameter of the curved part can be determined for each case. The most favorable construction is obtained if this cross-section is made exactly 10 of such a size that the curved part assumes the same temperature as the straight parts of the tube. However, a considerable portion of this effect can be obtained by giving the narrower part a cross-section that difiers somewhat from the 15 most favorable value. In most cases, the crosssection of the curved part of the tube is made at least 10 per cent smaller than the cross-section of the straight parts.

In the drawing accompanying and forming part 20 of this specification an embodiment of the invention is shown in a front elevational view.

Referring to the drawing the new and novel gaseous electric discharge lamp device comprises an elongated, tubular container whichhas two straight parts I and 2 which are connected by a curved part 3. In the upper ends of the parts I and 2, electrodes are arranged, namely a cathode 4 which is a metal filament, such as a tungsten filament, coated with an electron emitting material, such as barium oxide, and which is electron emitting when heated and a cylindrical anode 5. The current-supply wire of this anode 5 is connected inside or outside the tube with one of the current-supply wires of the cathode 5. The internal cross-section of the part 3 is considerably smaller than those of .parts I and 2 of the tube. It the internal diameter of the straight parts I and 2 is for instance 20 mm., the internal diameter of the curved part 3 is for instance l0 mm. The voltage gradient is, therefore, larger in part 3 than in the straight parts of the tube, so that in the first-mentioned part,

a larger amount of power is consumed per unit of length than in the other part of the tube. The heat given oif by part 3, however, is also larger than that emitted by parts I and 2. The cross-section of the curved part can, therefore, be selected in such a way that the temperature in this part is equal to that in the other part of the tube.

The tube contains a rare, starting gas, such as neon, and the vapor of a dimcultly vaporizable material, such as sodium. .The metal vapor participates in the discharge which takes place in the tube which should not always be considered as, meaning that'the metal vapor carries a part of the ,current. Under certain circumstances, it is also possible that the metal-vapor molecules, without participating in the current conduction, are merely excited and emit light. As a result of the uniform temperature oi! the wall of the tube, the required vapor pressure will be obtained in a very favorable manner which contributes to a considerable extent to the increase oi the eiilciency of the discharge tube.

The above described lamp device is ,mounted in a heat conservator i which is a double-walled Jacket having the space between the walls evacuated or filled with a gas having poor heat conductivity characteristics at a pressure lower than atmospheric pressure. It will be understood, of course, that the space between the jacket and the lamp container is closed 01! from the outside atmosphere by a body of heat insulating material, such as asbestos, and that a base is provided for the heat conservator and the lamp therein to form a complete lamp unit. These elements have been omitted from the drawing for purposes of simplicity of illustration.

While we have shown and described and have pointed out in the annexed claims certain novel features 01 the invention, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its use and operation may be made by those skilled in the art without departing from the broad spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:-

a l. A lamp unit comprising in combination, a gaseous electric discharge lamp device comprising an elongated, tubular sealed container, a gaseous'atmosphere therein comprising a metal vapor, electrodes sealed therein, a heat conservator in operative relation to said lamp device, said container having straight parts and a curved part connecting said straight parts, the inside diameter of said curved part being less than the internal diameter of said straight parts.

2. A lamp unit comprising in combination, a gaseous electric discharge lamp device comprising an elongated, tubular, sealed container, a gaseous atmosphere therein comprising a metal vapor, electrodes sealed therein, a-heat conservator in operative relation to said lamp device, said container having straight parts and a curved part connecting said straight parts, the inside diameter of said curved part being at least 10% leslsts than the internal diameter of said straight pa 3. A lamp unit comprising in combination, a gaseous electric discharge lamp device comprising an elongated, tubular, sealed container, a gaseous atmosphere comprising a rare, starting gas and a metal vapor, electrodes sealed therein, a heat conservator in operative relation to said lamp device, said container having straight, parts and a curved part connecting said straight parts, the inside diameter of said curved part being less than the internal diameter oi! said straight parts.

4. A lamp unit comprising in combination, a gaseous electric discharge lamp device comprising an elongated, tubular, sealed container, a gaseous atmosphere therein comprising a rare, starting gas and sodium vapor, electrodes sealed therein, a heat conservator in operative relation to said lamp device, said container having straight parts and a curved part connecting said straight parts, the inside diameter of said curved part being less than the internal diameter or said straight parts.

WILLEM UYTERHOEVEN.- CORNELIS V'ERBURG. 

